That's because it's logical that implementing network capable segmentation and flow control is more costly than just moving data with internal, native structures. And looking up random benchmarks yields anything from equal performance to 10x faster for Unix domain.

Unix Domain Sockets are the standard mechanism for app->sidecar communication at Google (ex: Talking to the TI envelope for logging etc.)

Are there resources suggesting otherwise?

As often in computing, profiling is a foreign word.

Tell me more, I know nothing about IPC